U.S. Pat. Nos. 2,348,350; 3,068,926; 3,620,279; and 3,780,782, show and describe tires in which breaker strips are embedded within the carcass plies of the tire for the purpose of eliminating separation of the edges of the breaker strips from the carcass plies, as frequently happens when the breaker strips are together, apart from the carcass plies; i.e. a plurality of breaker strips are interposed between the tread and radially outermost carcass ply of the tire. The invention is directed to an improvement in such tires.
Briefly stated, the invention is in a bias tire having a number of carcass plies, each of which are reinforced with textile cords of the group of rayon, nylon, and polyester. A pair of breaker strips or plies, reinforced with high modulus cords of the group of materials of steel and aromatic polyamide, preferably with steel cords, are embedded in the carcass plies in the area of the tread of the tire. The angular orientation of the high modulus cords of the breaker strips is substantially the same as that of the textile cords of the carcass plies. The width of each breaker strip is less than the width of the tread of the tire. According to a preferred feature a cap ply in the form of a single layer of textile cords of the group of rayon, nylon and polyester, covers the breaker strips and carcass plies in the area of the tread. The lateral edges of the cap ply extend into the sidewalls of the tire.
It was found that the improved tire structure increased the bruise resistance and, quite unexpectedly, the mileage of the tire by more than 50 percent. Thus, it can be appreciated that with the same rated load and speed, fewer carcass plies can be utilized, thereby providing increased flexibility for the sidewalls of the tire. More specifically, it has been found that problems with tread cracking and rapid shoulder wear as experienced with conventional tires without the breaker strips according to the invention, but designed for the same rated load and speed, are avoided by the tire structure of the invention, which results in a regular and even tread wear. Though the above surprising improvements have been also obtained with tires according to the invention wherein the breaker strips have cords of aromatic polyamide, it is presently preferred to use steel cords in the breaker strips. With steel cords in the breaker strips mileage improvements in the range between 60 and 100 percent could be achieved and average mileages up to some 50,000 miles in heavy road transport can be achieved for instance with 18-19.5 Super Single tires of the construction of the invention Super Single is a trademark of The Goodyear Tire & Rubber Company.